In an X-ray inspection system, an X-ray emitting device is mainly an electron accelerator or an X-ray tube. The X-ray emitting device and a detector array adopted to receive X-ray are placed on both sides of an inspected object. Under normal circumstances, an X-ray beam emitted by the X-ray emitting device contains both a working beam directly irradiated on the detector array and a redundant beam irradiated on the outside of the detector array.
The X-ray beam is usually a fan-shaped beam, the fan-shaped beam is perpendicular to the ground, and the width of the working beam in the fan-shaped beam at the detector array is generally required to be approximately equal to the width of the detector array. For this reason, a collimator is often arranged between the X-ray emitting device and the detector array. The collimator is adopted to shield the redundant beam in the X-ray beam. When an object is inspected, the collimator is located between the X-ray emitting device and the inspected object.
In general, the intensity of the X-ray beam is monitored by means of dose monitoring or brightness monitoring of the X-ray beam. Dose monitoring means monitoring the dose intensity of the X-ray beam, judging whether the dose intensity exceeds a regulated dose value, and if so, and sending a dose monitoring signal to perform such operations as alarming or cutting off the power supply of the X-ray emitting device and the like. Brightness monitoring means collecting a fluctuation change value of the intensity of the X-ray beam within each measurement period and sending a brightness correction signal to correct the value collected by the detector array, so as to obtain more accurate information of the inspected object.
A dose monitoring device and a brightness monitoring device of the X-ray beam are common in the X-ray inspection system, and the two devices independently exist in the X-ray inspection system under normal conditions.
The X-ray inspection system and the X-ray beam intensity monitoring device thereof in the prior art will be illustrated below by taking it as an example that the electron accelerator is used as the X-ray emitting device of the X-ray inspection system.
The dose monitoring device in the prior art includes a detecting module, the detecting module is directly placed at the outlet of the X-ray beam of the electron accelerator in general and is located in a box body of the electron accelerator, X-rays directly penetrate through the sensitive volume of the detecting module and irradiate on the inspected object.
The monitoring method adopted by the brightness monitoring device in the prior art is to collect a brightness signal by using a redundancy detector at the upper edge region of the fan-shaped beam in the detector array for X-ray inspection and send the brightness correction signal to correct the value collected by the detector array.
In a process of implementing the present invention, the inventor of the present invention finds that the above prior art has the following disadvantages:
in the dose monitoring device in the prior art, the X-ray beam intensity is lost because of the necessity of penetrating through the sensitive volume of the detecting module, namely, the detecting sensitive volume intervenes in the X-ray beam intensity and a structure of energy spectrum arriving at the inspected object. Moreover, since the electron accelerator is a heavy current installation, while the detecting module of the dose monitoring device is a weak current instrument, the detecting module is very susceptible to electromagnetic interference of the former, and can only provide average dose information within a certain period of time in general, for example, a few seconds. In the X-ray inspection system, to ensure safety, when the dose of the X-ray beam is larger than a regulated threshold, the power supply of the X-ray emitting device must be cut off as soon as possible, thus the dose monitoring device is required to be reliable and accurate in measurement, but the dose monitoring device in the above prior art is difficult to satisfy this requirement.
In the brightness monitoring device in the prior art, the redundancy detector of the detector array is susceptible to interference of a reflected signal, mechanical deformation and other factors of the inspected object. Moreover, when the X-ray emitting device is the electron accelerator, the X-ray beam intensity on the “main beam” direction (i.e., the direction of the electron beam) of the X-ray beam is large, the larger the included angle of a position with the “main beam” is, the weaker the X-ray beam intensity is, and the X-ray beam intensity of the region where the redundancy detector is located is generally weak, so that the monitoring result is affected ultimately.